The present invention relates to electrical membrane switches and in particular to a membrane switch having or adhered to a substantially rigid front surface or fascia.
Membrane switches are well known in the art and normally employ a pair of stacked flexible membranes having opposed contacts printed on their facing surfaces. A spacer layer separates the membranes, except at a region about the contacts, allowing pressure from a finger or the like to deform one of the membranes so that its contact touches the contact of the other membrane closing an electrical switch. The natural resilience of the membranes may separate the contacts once the force of closure is removed. Electrical conductors, also printed on the facing surfaces of the membranes, communicate electrical signals to and from the contacts.
Normally, a thin plastic decorative trim is adhered to the front surface of the membrane switch to indicate the position of the buttons and their functions to the user.
A single membrane may support many contacts making membrane switches a cost effective solution for multi-switch control panels and the like. The continuous front membrane of a membrane switch seals the switch contacts from contamination, and for this reason, membrane switches are often used in environments where moisture or contaminants are a problem.
Membrane switches have some drawbacks. While the membrane itself is resistant to contamination and readily cleaned, it is soft and susceptible to abrasion or damage. The membranes must often be applied over the outer housing of an appliance or other device where they are exposed to damage. The common look and feel of thin plastic membrane can be limiting to designers experimenting with a wider range of design aesthetics.
The problem of damage to the membranes is addressed in U.S. Pat. No. 5,747,757 to Van Zeeland which describes positioning a membrane switch behind a thin panel of metal to resist vandals. Van Zeeland also suggests alternative use of plastics such as Lucite, Kevlar, or glass. As noted by Van Zeeland, the rigid panel tends to spread the force of actuation by a finger, or the like, over a broader area creating a risk that adjacent switches will be simultaneously actuated by a single touch. Van Zeeland addresses this problem using rigid standoffs or similar structures between the front panel and a back support that resists the deflection of the front panel except at the contact areas, thereby attempting to focus the deflection of the front panel to the contact areas.
Limiting the natural deflection of the front panel increases the force required to deflect the front panel to an amount which may be unacceptable to the average user.
The standoff system proposed by Van Zeeland also increases the complexity of manufacture of the membrane switch requiring specialized mechanical components that must be changed for each changed layout of the switch. The problems of supporting these standoffs against the minor deflections they must resist presents additional barriers to the use of the Van Zeeland design.